In general it means parking of transaction, waiting threads for callback or free thread pool, or thread locks. You should dive into method hotspot and find right place for analysis there. Sometimes it is possible to find good candidate for extra instrumentation using request attributes 🙂
About how to resolve this issue it’s not easy question. It depends of nature. Sometimes you need to check how some libraries used for external communication works to determine why they are parking transaction. This may be because external resource / server is responding too slow, thread pool is exhausted and process is locking itself. But this is one of many possibilities.